Recently, portable electronic products such as a camcorder, a portable phone and a notebook personal computer have been generally used with the rapid development of electronic, communication and computer industries, so light, long-lifetime and high-reliable batteries have been demanded.
In particular, secondary batteries such as nickel-hydrogen (Ni-MH) secondary batteries and lithium secondary batteries have been markedly demanded. In particular, the lithium secondary batteries using lithium and a non-aqueous solvent electrolyte can be realized as batteries having small, light and high-energy density characteristics, so they are actively being developed.
Generally, the lithium secondary battery is formed using a transition metal oxide (e.g., LiCoO2, LiNiO2, or LiMn2O4) as a cathode material, using lithium metal or carbon as an anode material, and using an organic solvent containing lithium ions as an electrolyte disposed between the two electrodes.
If the lithium secondary battery using the lithium metal as the anode is repeatedly charged and discharged, dendrite may be easily generated to cause an electrical short. Thus, a lithium secondary battery using a carbonized or graphitized carbon material as the anode and using the non-aqueous solvent as the electrolyte has been commercialized.
However, the graphitized carbon material may have a theoretical lithium storage capacity of 372 mAh/g, which corresponds to 10% of a theoretical capacity of the lithium metal. In other words, the graphitized carbon material has a very small capacity. Thus, researches have been conducted for materials having a greater lithium storage capacity than graphite.
A silicon-based material has been spotlighted because of its high capacity (4200 mAh/g). However, a volume variation (shrinkage or expansion) of the silicon occurs during insertion/de-insertion of lithium ions, so the mechanical stability of the silicon may be deteriorated. This means that a cycle characteristic of the battery is deteriorated. Thus, it is required to develop materials capable of improving structural stability and a cycle characteristic when used as an active material of an electrochemical device.
Recently, to solve these problems, researches have been focused on development of metal alloy-based anode materials capable of having a higher capacity and an excellent lifetime characteristic and of being substituted for a conventional carbon-based anode or lithium metal anode. Capacities of metal alloy-based anode materials such as tin (Sn), silicon (si) and germanium (Ge) may be two or more times greater than that of the conventional carbon-based material. However, since performance of the electrochemical device using the metal alloy-based anode active material is greatly affected by a manufacturing method or a structure of the composite, it is required to develop a new manufacturing method capable of improving the performance of the electrochemical device.